Compositions for filling dental cavities presently available usually comprises of dental alloys mixed with mercury. The dental alloys include at least three metals. A typical alloy would include Silver, Tin and Copper. Small percentages of one or more additional metals like Zinc, Indium, Palladium and the like metals may be added. These dental alloys are available either in fine powder or as tablets (i.e. compressed powder). The dental alloy is mixed with mercury to form a putty or plastic mass known as amalgam which is packed into a tooth cavity as a filling. Among the three metals, namely Silver, Tin and Copper, Silver is the only metal used in dental alloys that can completely react with mercury to form a silver-mercury compound or silver amalgam.
Recently research scientists have established that there is "free" mercury i.e. unreacted mercury present within the amalgam fillings in the mouth. The free mercury can vapourise in the mouth from the fillings due to the higher temperatures experienced in the mouth. The mercury vapour can be inhaled into the lungs, where it is absorbed into the bloodstream. Studies have shown deposits of mercury in brain and kidney tissues that have originated from such fillings. Mercury also causes bleeding gums and skin reactions.
This "free" mercury has contributed to various medical problems as well as in certain patients, hypersensitivity reactions. In fact, in recent times, dental experts in Sweden have recommended to the authorities to ban the use of such "amalgams" in pregnant women to prevent genetic damage to the fetus as there is evidence to show that "free" mercury from the mother can via the transplacental route, affect the fetus.
A lesser problem in the use of conventional dental alloy amalgams is the chemical corrosion caused in the oral cavity. As tin and copper are prone to corrosion, the corrosion process continues in the mouth throughout the relatively short span of the life of the fillings.
In another aspect of the history of amalgam in dental fillings, silver fillings were mixed with mercury to form a putty which was filled into the tooth cavity. Unfortunately the mixed amalgam due to expansion property upon setting caused severe pain to the patient and protruded from the surface of the cavity and in bad cases even fractured the crowns of the teeth. In either case, the patient suffers severe pain, resulting in the extraction of the tooth. For this reason, silver in the original is not used alone with mercury to form the amalgam.
Tin is added to silver to make an alloy of silver and tin which alloy is then mixed with mercury to form the amalgam. Tin causes contraction on setting. This contraction can be offset by the expansion property in the purely silver-mercury amalgam. But the main disadvantage is that the mercury in the resultant amalgam contains unreacted mercury (in the free state) within the fillings.
To increase the strength of the amalgam filling varying percentage of copper was added to silver-tin alloy. Unfortunately the resultant amalgam still has mercury in the free state. As stated before, mercury vapour formation within the mouth can cause ill-effects to the patient.
Simply stated, for more that 150 years the search for a dental amalgam that is devoid of the toxic and harmful effect of free mercury has eluded researches.